Nearly 8,000 Which? members this year responded to the watchdog’s annual airline survey.

The budget carrier received the lowest possible rating for boarding, seat comfort, food and drink and cabin environment, amassing an overall score of just 40%.

Aurigny Air Service, Swiss Air, Jet2.com, Norwegian and KLM made up the top five.

A Ryanair spokesperson said the survey was ”unrepresentative” and failed to recognise its popularity and growth.

When asked to name one airline with whom they would never travel, 70% of respondents to the Which? survey named Ryanair, even if it was cheaper than rival airlines.

According to Which?, Ryanair made £1.75 billion in “extras” last year, some 28% of its revenue. This included assigned seating, priority boarding and additional luggage costs.

The airline altered its luggage rules several times last year, which passengers said had caused confusion.

One respondent said: “There are too many rules. I worry about getting caught with hidden costs.”

Ryanair’s schedule was also hit by pilot and cabin crew strikes, which the CAA ruled did not amount to “extraordinary circumstances”, meaning the airline should be liable to pay passengers EU261 compensation. It has so far refused and is now facing enforcement action from the CAA.

After scoring just 52% last year for its short-haul service and 50% for long-haul, British Airways promised improvements but was still only able to improve to 56% and 58% respectively.

EasyJet came in with a middling 63% while Jet2.com impressed with its service, seating and boarding provision, scoring 75%.

Airlines were rated for boarding, seat comfort, food and drink, cabin environment customers service and value for money. The lowest possible rating for each of these areas is a one star rating.

Which? travel editor Rory Boland said: “Airfares might seem to be getting cheaper, but only if you don’t fancy sitting with your family and children or taking even a small cabin bag on-board. Increasingly you need a calculator to work out what the final bill will be, especially with Ryanair.

“It has spent the last two years cancelling thousands of flights, ruining hundreds of thousands of holidays and flouting the rules on compensation as well. The results of our survey show passengers are fed up. They should switch to one of their rivals, who prove that budget prices don’t have to mean budget service.”

In a statement provided to Which?, Ryanair denied it had experienced significant problems as a result of the 2018 strikes, arguing 90% of schedules remained operational on strike days.

It also said ‘it delivers industry-leading customer service’ and claimed its bag policy had been ‘simplified’ by recent changes.

Ryanair claimed decreased punctuality in 2018 was largely due to air traffic control strikes, adding: “We’ve invested heavily in delivering on-time departures.”

The airline also insisted passengers would continue to book with Ryanair as “having the lowest prices wins every time”.

A Ryanair spokesperson added: "Ryanair passenger numbers have grown by 80% in the past six years and Ryanair.com has become the world’s most visited airline website.

"These facts reflect what customers want much more than an unrepresentative survey of just 8,000 people."